Gas Dissolution Research Articles

Difference Analysis of Gas Molecules Diffusion Behavior in Natural Ester and Mineral Oil Based on Molecular Dynamic Simulation

Natural ester, as a new environmentally green insulating oil, has been widely used in transformer. In an oil-immersed transformer, the normal aging, thermal failure, and discharge failure could easily lead to the decomposition of the oil-paper insulation system and produce different kinds of gases. Studying gas dissolution in natural ester and mineral oil could provide assistance in applying criteria to make a diagnosis of different kinds of faults in the transformer. In this paper, the molecular dynamics method was used to investigate the diffusion behavior of seven fault characteristic gases (including H2, CO, CH4, C2H2, CO2, C2H4, C2H6) in natural ester and mineral oil. The simulation parameters of free volume, interaction energy, mean square displacement, and diffusion coefficient were compared between the natural ester and mineral oil. Meanwhile, the influence of temperature on the diffusion of gas molecules in two kinds of oils was also analyzed. Results showed that the free volume, the interaction energy, and the relative molecular mass of gas molecules were the factors influenced by the diffusion of gas molecules in natural ester and mineral oil. The order of the diffusion coefficients of gas molecules in natural ester was as follows: H2 > CH4 > CO > C2H2 > C2H4 > CO2 > C2H6 and that in mineral oil was as follows: H2 > CH4 > CO> C2H2 > C2 H4 > C2H6 > CO2. By comparing the diffusion behavior of gas molecules in natural ester and mineral oil, it was found that the smaller free volume and higher interaction energy of gas molecules in natural ester were the major reasons for the gas molecules to be more difficult to diffuse in natural ester. The rising temperature could enhance the free volume and reduce the interaction energy between gas molecules and oil. The diffusion coefficient of gas molecules increased exponentially with the follow of temperature. However, the temperature didn’t affect the ordering of diffusion coefficient, free volume, and interaction energy of gas molecules in natural ester and mineral oil.

Impact of undissolved gas on dynamic processes in the fluid drive for well testing and servicing research

This paper concerns topical issues because power oils for a hydraulic drive are the mixture of liquid and undissolved gas. This mixture can arise when tanking and during dynamic processes because of the different dissolution and evolution rates of gas in a pressure fall in some spots of power fluid flow. That is why this paper deals with the impact of the gas factor on the behavior pattern of fluid. When describing the processes fluid drive was considered as a lumped parameters system.

Thermodynamic limits on cell size in the production of stable polymeric nanocellular materials

The reduction of cell size to the nanometre scale is one of the main current focuses in polymeric cellular materials research. The recent achievement of cell sizes in the range of 10–200 nm naturally gives rise to the question of what are the main limiting factors in obtaining further improvements. This paper explores the theoretical limits of this reduction in scale size, and presents an application of atomistic modelling strategies for the study of nanofoams produced by the gas dissolution technique. The main conclusion is that, as the cell size scale becomes closer to molecular sizes, atomic-scale interactions should be considered, and conventional rules for foams usually applied to continuous media should be reassessed due to the increasingly discrete nature of the polymeric material. The gas-polymer equilibrium for a range of different polymers (HDPE, PP, PVDF, PEI, PS, PES, PC and PMMA) were calculated using molecular dynamics (MD), in order to generate structures in the nanometric range and to study their stability. The results show that the minimum stable cell size is governed by the behaviour of the internal pressure in the polymer within small gas-filled voids, which may explain the differences between cell sizes observed experimentally in different polymers.

Influence of the viscosity of poly(methyl methacrylate) on the cellular structure of nanocellular materials

AbstractThree different grades of poly(methyl methacrylate) (PMMA) with different rheological properties are used for the production of nanocellular materials using gas dissolution foaming. The influences of both the viscosity of the different polymers and the processing parameters on the final cellular structure are studied using a wide range of saturation and foaming conditions. Foaming conditions affect similarly all cellular materials. It is found that an increase of the foaming temperature results in less dense nanocellular materials, with higher cell nucleation densities. In addition, it is demonstrated that a lower viscosity leads to cellular polymers with a lower relative density but larger cell sizes and smaller cell nucleation densities, these differences being more noticeable for the conditions in which low solubilities are reached. It is possible to produce nanocellular materials with relative densities of 0.24 combined with cell sizes of 75 nm and cell nucleation densities of 1015nuclei cm−3using the PMMA with the lowest viscosity. In contrast, minimum cell sizes of around 14 nm and maximum cell nucleation densities of 3.5 × 1016nuclei cm−3with relative densities of 0.4 are obtained with the most viscous one. © 2019 Society of Chemical Industry

Mathematical Model of Gas Dilution in Two Phases Flows of Fluid and Gas

Various models of solubility of gas in two-phase ows of gas and liquid are considered. Such phenomena play an important role in various technical devices especially at modern nuclear power plants. Mathematical models of bubble ows with gas dissolution, gas phase model, and model of liquid phase dissolution were considered and discussed.

METHOD OF GAS PRESSURE OPTIMIZATION IN PRODUCING WELL ANNULUS

The process of oil production using sucker rod-pumping installations, especially with high gas content of formation fluid, is accompanied by accumulation of oil gas in the annulus of wells. The growth of the annular gas pressure causes an increase in the back pressure on the reservoir and a number of other negative consequences, to exclude which various technologies are used to pump out gas from the annular space of production wells. The article considers the problem of optimizing the gas pressure in the annulus by pumping gas with a compressor at a constant speed. The design of the suspended plunger compressor driven by the balance of the pumping unit and the method for calculating the technological parameters of the compressor based on the balance of the compressor supply and the volumetric flow rate of the separated gas into the annulus are proposed. A two-stage algorithm for calculating the parameters of the optimal technological mode of well operation has been developed. As an optimization criterion, joint fulfillment of the following conditions was proposed: ensuring the permissible volume fraction of gas at the inlet, minimum pump immersion under the dynamic level, and maximizing the flow rate of the well. To assess the effectiveness of the proposed well operation technology and to calculate the increase in well flow rate during compressor operation, a mathematical model of a multiphase stationary gas-liquid mixture flow in a wellbore operated by a pumping pump unit, taking into account the equilibrium processes of separation and dissolution of oil gas, the effects of oil and gas phase slip, is proposed. The calculation results confirm that the use of compressors for pumping gas from the annulus allows one to obtain a significant increase in the flow rate of liquid and oil, which depends on the parameters and properties of the pumped product, the operational characteristics of the formation and barothermal conditions.

Development of bio-based poly(butylene succinate) formulations for microcellular injection foaming

Manufacturing lightweight plastic parts with high productivity while maintaining a high level of quality and excellent reproducibility of cellular structure reduces the amount of raw material needed while improving the carbon balance thanks to the bio-sourced origin of the polymer and the decrease of the transported mass. In this study, structural modifications of PBS were carried out in order to control the foaming mechanism in each phase of cell formation (gas dissolution, cell nucleation, cell growth and cell stabilization). Cell morphology has been improved by modifying the molecular architecture (ramified/branched, semi-reticulate structures), promoting nucleation (decrease of surface tension leading to a decrease in Gibbs’s energy barrier), or by adjusting the extensional viscosity or Newtonien viscosity of the material. The resulting formulation exhibits a decrease of more than 80% in cell size and a cell density multiplied by 450 regarding the linear structured injection moulding PBS reference FZ71 (Mitsubishi Chemical Corporation (MCC), Japan) noted here L-PBS.

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

AbstractGraded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low‐density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt‐blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano‐ to micron‐sized cells. This gradient structure is attributed to a non‐constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained.

Organ preservation solution containing dissolved hydrogen gas from a hydrogen-absorbing alloy canister improves function of transplanted ischemic kidneys in miniature pigs.

Various methods have been devised to dissolve hydrogen gas in organ preservation solutions, including use of a hydrogen gas cylinder, electrolysis, or a hydrogen-generating agent. However, these methods require considerable time and effort for preparation. We investigated a practical technique for rapidly dissolving hydrogen gas in organ preservation solutions by using a canister containing hydrogen-absorbing alloy. The efficacy of hydrogen-containing organ preservation solution created by this method was tested in a miniature pig model of kidney transplantation from donors with circulatory arrest. The time required for dissolution of hydrogen gas was only 2-3 minutes. When hydrogen gas was infused into a bag containing cold ETK organ preservation solution at a pressure of 0.06 MPa and the bag was subsequently opened to the air, the dissolved hydrogen concentration remained at 1.0 mg/L or more for 4 hours. After warm ischemic injury was induced by circulatory arrest for 30 minutes, donor kidneys were harvested and perfused for 5 minutes with hydrogen-containing cold ETK solution or hydrogen-free cold ETK solution. The perfusion rate was faster from the initial stage with hydrogen-containing cold ETK solution than with hydrogen-free ETK solution. After storage of the kidney in hydrogen-free preservation solution for 1 hour before transplantation, no urine production was observed and blood flow was not detected in the transplanted kidney at sacrifice on postoperative day 6. In contrast, after storage in hydrogen-containing preservation solution for either 1 or 4 hours, urine was detected in the bladder and blood flow was confirmed in the transplanted kidney. This method of dissolving hydrogen gas in organ preservation solution is a practical technique for potentially converting damaged organs to transplantable organs that can be used safely in any clinical setting where organs are removed from donors.

Effects of phase transitions on nonstationary liquid-gas flow in a well during gas kicks

The paper presents a model of nonstationary liquid-gas flow in a well considering non-equilibrium phase transitions. The problem is topical for Managed Pressure Drilling (MPD) with lightweight oil-based mud in case of a gas kick. The model accounts for the relaxation character of gas dissolution and separation at phase transitions in the liquid-gas system. A numerical solution method has been proposed, which is based on the kinematic-wave model. The paper provides examples of gassy and bubbly area evolution and hydrodynamic flow parameters during a gas kick. The effect of backpressure on the velocity of gas kick and bottomhole pressure has been analyzed. It has been demonstrated that consideration of phase transitions considerably affects the gas kick process and the bubbly-gassy area rising to the wellhead.

Production of PMMA-based nanocellular polymers using low demanding saturation conditions

Abstract Nanocellular polymers are novel materials characterized by nanometric cell sizes with huge potential in many industrial applications. However, their production is challenging and usually requires demanding processing conditions that make difficult the production at industrial scale. In this work, we prove that nanocellular polymers based on PMMA can be obtained, thanks to the addition of nucleating species, using low saturation pressure (6 MPa) and room saturation temperature in a gas dissolution foaming process. Nanoparticles and block copolymers at different concentrations are used to obtain a collection of nanocellular polymers with densities ranging 0.16–0.58 and cell sizes from 120 to 900 nm. Comparison with the literature results shows that the processing parameters used in this work are the less demanding ever used for producing nanocellular PMMA.

Investigation of the effects of Al nanoparticles on CO2 separation from natural gas using gas hydrates

ABSTRACT The low hydrate formation rate, the low gas selectivity and the low gas storage capacity have been proved as the major bottlenecks for a successful application of CO2 capture process using gas hydrates. Aluminum nanoparticles has an important specific area, which can lead to high heat and mass transfer efficiency, large gas dissolution, fast nucleation, and formation rate. In this work, CO2-CH4 hydrate formation with and without aluminum nanoparticles was investigated. Herein, the promoting mechanism and effects of aluminum nanoparticles concentrations for an initial pressure of 4.0 MPa and temperature of 274.15 K on CO2-CH4 hydrate formation process were studied experimentally. The obtained results showed that the nanoparticles of Al, beyond a certain minimum concentration, slightly enhanced the gas dissolution, notably improved the gas consumption by crystallization and dramatically improved the gas capture selectivity. These positive effects were observed at the beginning of the process and after that became negative.

Methane Source and Turnover in the Shallow Sediments to the West of Haima Cold Seeps on the Northwestern Slope of the South China Sea

The Haima cold seeps are active cold seep areas that were recently discovered on the northwestern slope of the South China Sea (SCS). Three piston cores (CL30, CL44, and CL47) were collected within an area characterized by bottom simulating reflectors to the west of Haima cold seeps. Porewater profiles of the three cores exhibit typical kink-type feature, which is attributed to elevated methane flux (CL30) and bubble irrigation (CL44 and CL47). By simulating the porewater profiles of SO42-, CH4, PO43-, Ca2+, Mg2+, and dissolved inorganic carbon (DIC) in CL44 and CL47 using a steady-state reaction-transport model, we estimated that the dissolved SO42- was predominantly consumed by anaerobic oxidation of methane (AOM) at rates of 74.3 mmol m−2 yr−1 in CL44 and 85.0 mmol m−2 yr−1 in CL47. The relatively high AOM rates were sustained by free gas dissolution rather than local methanogenesis. Based on the diffusive Ba2+ fluxes and the excess barium contents in the sediments slightly above the current SMTZ, we estimated that methane fluxes at core CL44 and CL47 have persisted for ca. 3 kyr and 0.8-1.6 kyr, respectively. The non-steady-state modeling for CL30 predicted that a recent increase in upward dissolved methane flux was initiated ca. 85 yr ago. However, the required time for the formation of the barium front above the SMTZ at this core is much longer (ca. 2.2-4.2 kyr), which suggests that the depth of SMTZ possibly has fluctuated due to episodic changes in methane flux. Furthermore, using the model-derived fractions of different DIC sources and the δ13CDIC mass balance calculation, we estimated that the δ13C values of the external methane in cores CL30, CL44, and CL47 are -74.1‰, -75.4‰, and -66.7‰, respectively, indicating the microbial origin of methane. Our results suggest that methane seepage in the broader area surrounding the Haima cold seeps probably has persisted at least hundreds to thousands of years with changing methane fluxes.

Sequential Slope and Intercept Method for Estimation of Gas Absorption and Diffusion Coefficients in Binary Gas–Liquid Systems

A novel geometric method based on a sequential slope–intercept approach is derived for estimation of concentration-dependent diffusion, gas absorption, and gas dissolution concentration in gas–liquid binary systems. The gas absorption and diffusion are modeled using an inverse free boundary problem governed by Fick’s second law of diffusion and Henry’s absorption law. An unknown gas–liquid interface is governed by the Stefan’s type boundary condition. Implementation of the estimation method involves piecewise linear approximation of the transformed concentration data and sequential application of the estimated slopes and intercepts from this approximation. Application and validation of the developed estimation method is given for synthetic concentration profiles and for real concentration measurements for a dimethyl ether–bitumen binary system obtained using computer tomography. The developed estimation method overcomes the existing estimation methods derived from polynomial approximations that significantly underestimate or overestimate the diffusion coefficients at very low dissolved gas concentrations.

Enhanced photoreduction of CO2 into methanol by facet-dependent Cu2O/reduce graphene oxide

The preparation of cuprous oxide (Cu2O) with different morphologies and oxidation states decorating with reduced graphene oxide (rGO) and their comparison in the photocatalytic reduction of CO2 are reported in the present work. The rhombic dodecahedra Cu2O/rGO exhibits the highest methanol yield (355.3 μmol g−1cat) which is ca. 4.1–80.8 times superior to cubic, octahedral Cu2O/rGO and CuO/rGO after 20 h of visible light illumination. The enhanced performance may be due to the unique rhombic dodecahedra structure with less band bending of conduction and valence bands which decrease the energy barrier for the transfer of photogenerated electrons to the surface. The incorporation of rGO should assist the transfer of photogenerated electrons from conduction band of Cu2O. The positively charged dodecahedra Cu2O/rGO may also increase the adsorption of carbonate anions from dissolution of CO2 gas. This work provides a facile solution-chemistry route to synthesize rGO incorporated crystal Cu2O with various facets as visible-light-active photocatalysts for CO2 utilization by using natural sunlight.

Effects of Gas Adsorption on the Mechanical Properties of Amorphous Polymer.

This study investigates the properties of a polymer–gas mixture formed through diffusion, based on the changes in the partial pressure and observed changes in the impact and tensile strengths owing to the gas dissolution. The high-pressure gas dissolves into a solid-state polymer through diffusion based on the difference in the partial pressure. This dissolved gas is present in the amorphous region within the polymeric material temporarily, which results in the polymer exhibiting different mechanical properties, while the gas remains dissolved in the polymer. In this study, the mechanical properties of amorphous polyethylene terephthalate (APET) specimens prepared by dissolving CO2 using a high-pressure vessel were investigated, and the resulting impact and tensile strengths were measured. These experiments showed that the increase in sorption rate of CO2 caused an increase in the impact strength. At 2.9% CO2 absorption, the impact strength of APET increased 956% compared to that of the reference specimen. Furthermore, the tensile strength decreased by up to 71.7% at 5.48% CO2 sorption; the stress–strain curves varied with the gas sorption rate. This phenomenon can be associated with the change in the volume caused by CO2 dissolution. When the APET absorbed more than 2.0% CO2 gas, sample volume increased. A decrease in the network density can occur when the volume is increased while maintaining constant mass. The CO2 gas in the polymer acted as a cushion in impact tests which have sorption rates above 2%. In addition to the reduction in the network density in the polymer chain, Van Der Waals forces are decreased causing a decrease in tensile strength only while CO2 is present in the APET. These observations only occur prior to CO2 desorption from the polymer.

Overcoming the Challenge of Producing Large and Flat Nanocellular Polymers: A Study with PMMA

Although nanocellular polymers are interesting materials with improved properties in comparison with conventional or microcellular polymers, the production of large and flat parts of those materials is still challenging. Herein, gas dissolution foaming process is used to produce large and flat nanocellular polymethylmethacrylate samples. In order to do that, the foaming step is performed in a hot press. The methodology is optimized to produce flat samples with dimensions of 100 × 100 × 6 mm3, relative densities in the range 0.25–0.55 and cell sizes around 250 nm. Additionally, foaming parameters are modified to study their influence on the final cellular structure, and the materials produced in this paper are compared with samples produced by using a most conventional approach in which foaming step is conducted in a thermal bath. Results obtained show that an increment in the foaming temperature leads to a reduction in relative density and an increase of cell nucleation density. Moreover, differences in the final cellular structure for materials produced by both foaming routes are studied, proving that although there exist some differences, the mechanisms governing the nucleation and growing are the same in both processes, leading to the production of homogeneous materials with very similar cellular structures.

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

AbstractThis work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 1013–1014 nuclei cm−3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites. © 2019 Society of Chemical Industry

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Gas hydrates, acting as a dynamic methane reservoir, store methane in the form of a solid phase under high-pressure and low-temperature conditions and release methane through the sediment column into seawater when they are decomposed. The seepage of methane-rich fluid (i.e., cold hydrocarbon seeps) fuels the chemosynthetic biota-inhabited surface sediments and represents the major pathway to transfer carbon from sediments to the water column. Generally, the major biogeochemical reactions related to carbon cycling in the anoxic marine sediments include organic matter degradation via sulfate reduction (OSR), anaerobic oxidation of methane (AOM), methanogenesis (ME), and carbonate precipitation (CP). In order to better understand the carbon turnover in the cold seeps and gas hydrate-bearing areas of the northern South China Sea (SCS), we collected geochemical data of 358 cores from published literatures and retrieved 37 cores and corresponding pore water samples from three areas of interest (i.e., Xisha, Dongsha, and Shenhu areas). Reaction-transport simulations indicate that the rates of organic matter degradation and carbonate precipitation are comparable in the three areas, while the rates of AOM vary over several orders of magnitude (AOM: 8.3-37.5 mmol·m-2·yr-1 in Dongsha, AOM: 12.4-170.6 mmol·m-2·yr-1 in Xisha, and AOM: 9.4-30.5 mmol·m-2·yr-1 in Shenhu). Both the arithmetical mean and interpolation mean of the biogeochemical processes were calculated in each area. Averaging these two mean values suggested that the rates of organic matter degradation in Dongsha (25.7 mmol·m-2·yr-1) and Xisha (25.1 mmol·m-2·yr-1) are higher than that in Shenhu (12 mmol·m-2·yr-1) and the AOM rate in Xisha (135.2 mmol·m-2·yr-1) is greater than those in Dongsha (27.8 mmol·m-2·yr-1) and Shenhu (17.5 mmol·m-2·yr-1). In addition, the rate of carbonate precipitation (32.3 mmol·m-2·yr-1) in Xisha is far higher than those of the other two regions (5.3 mmol·m-2·yr-1 in Dongsha, 5.8 mmol·m-2·yr-1 in Shenhu) due to intense AOM sustained by gas dissolution. In comparison with other cold seeps around the world, the biogeochemical rates in the northern SCS are generally lower than those in active continental margins and special environments (e.g., the Black sea) but are comparable with those in passive continental margins. Collectively, ~2.8 Gmol organic matter was buried and at least ~0.82 Gmol dissolved organic and inorganic carbon was diffused out of sediments annually. This may, to some extent, have an impact on the long-term deep ocean carbon cycle in the northern SCS.

Targeted delivery of hydrogen for the bioremediation of aquifers contaminated by dissolved chlorinated compounds

Dihydrogen (H2) gas injection is a promising option to enhance the reductive biodehalogenation of contaminants in groundwater. However, it is challenging to ensure its targeted delivery at the right places in plumes, and for the long times required for bioremediation. In this paper, the ability of surfactant foam to retain H2 in the saturated zone and to enhance its release in the dissolved form was compared to traditional biosparging. H2 gas was injected, either alone, or as foam, in a 2D saturated cell packed with glass beads. This cell was continuously flushed with deoxygenated water to mimic aquifer circulation, and H2 was studied both in terms of gas distribution in the cell and dissolved concentrations downstream the injection zone. Experimental results are discussed in conjunction with simulations obtained using modeling. Both show that the viscous behavior of foam allows to efficiently retain greater volumes of H2 gas, 3.5 times higher than biosparging. Moreover, it is retained in a dense manner around the injection point, making possible the targeted delivery of this reagent. Besides, the gas dissolution in groundwater showed to be steadier and more persistent when gas was injected as foam, with dissolution rate constants observed to be 1.12 à 1.58 times lower. Finally, the retained foamed-gas persistently reduced water's relative permeability 1.7 to 5 times, diverting the groundwater flow from the treated zone despite the fast elution of the surfactant. Hence, when H2-foam injection is targeted to plume's contaminant concentration hotspots, on top of enhancing bioremediation, it can reduce contaminant diffusion to groundwater.